This invention relates to a crawler belt suitable for use on crawler type vehicles, for example, on hydraulic excavators, hydraulic cranes and the like.
Generally, crawler belts which are used on crawler type vehicles such as hydraulic excavator and the like are largely constituted by rows of endlessly connected right and left track links each formed with an outer link portion and an inner link portion at longitudinally opposite ends, respectively, bushes located transversely between the right and left track links in such a way as to connect inner link portions of the respective track links with each other, connecting pins placed in the respective bushes and each having opposite ends thereof coupled with the outer link portions of the track links by fitting engagement therewith, and seal members provided on the outer peripheral side of the connecting pins between an outer link portion of a track link and a bush.
The prior art crawler belt of this sort is lapped around an idler wheel and a drive sprocket and rolled on in the forward or backward direction between and around the idler wheel and drive sprocket by a drive means such as hydraulic motor or the like to drive a vehicle body in a forward or reverse direction.
In order to prevent intrusion of soil or dust into gap spaces between bushes and connecting pins, it has been known in the art to provide an annular seal member of rubber or the like between an outer link portion of each track link and a bush (e.g., as disclosed in Japanese Patent Laid-Open No. H7-285472).
In the case of the prior art crawler belt seal as disclosed in the above-mentioned Japanese Patent Laid-Open No. H7-285472, a gap space between an outer link portion of a track link and a bush is sealed up by a seal member, thereby preventing dirt or other foreign matter from getting between bush and connecting pin.
However, once dirt gets into contacting surfaces of the seal member and bush, for example, it can accelerate abrasive wear of the contacting surfaces of these members to lower the seal effects of the seal member.
Besides, in such a case, there also arises a problem that, through a seal member, dirt can get into a gap space between a bush and a connecting pin to accelerate abrasive wear to inner peripheral surfaces of the bush and/or to outer peripheral surfaces of the connecting pin.
Further, dirt which has intruded into a gap space between a bush and a connecting pin tends to accumulate in the gap without being discharged to the outside, to hinder smooth relative rotations of the bush and connecting pin as well as smooth movements of the crawler belt.
In view of the above-discussed problems with the prior art, it is an object of the present invention to provide a crawler belt which can prevent soil or other foreign matter from getting into gap spaces or clearances between bushes and connecting pins of the crawler belt from outside, preventing abrasive wear of and damages to sliding surfaces of bushes and connecting pins which would be caused by the intrusion of foreign matter.
It is another object of the present invention to provide a crawler belt which can prevent accumulation of soil or other foreign matter in gap spaces or clearances between bushes and connecting pins of the crawler belt to ensure smooth relative rotational movements of the bushes and connecting pins over a long period of time.
In order to solve the above-discussed problems with the prior art, the present invention contemplates to provide a crawler belt of the sort which includes: endlessly connected right and left track links each formed with an outer link portion and an inner link portion at opposite longitudinal ends thereof; bushes transversely located between the right and left track links in such a way as to connect inner link portions of the respective track links with each other; connecting pins inserted in the bushes and having opposite end portions fitted in and connected to the outer link portions of the respective track links; and seal members fitted on the circumference of the connecting pins at positions between the outer link portions of the track links and the bushes.
The crawler belt according to the present invention is characterized by the provision of: a sliding bearing receptacle groove provided on and around an inner peripheral surface of each bush, and said sliding bearing receptacle groove having a diameter larger than said inner peripheral surface; a hardened surface layer provided at least on an inner peripheral surface of the bush or on an outer peripheral surface of the connecting pin to impart higher hardness thereto; and a resinous sliding bearing formed of a tubular synthetic resin material lower in hardness than the bush and fitted in the sliding bearing receptacle groove of the bush, the resinous sliding bearing having a slide surface on the inner peripheral side thereof in sliding contact with the connecting pin.
With the arrangements just described, by the resinous sliding bearing which is fitted in the sliding bearing receptacle groove on the inner peripheral surface of the bush, dirt or soil which gets between an outer link portion and a bush through the seal member during a vehicular driving operation of the machine can be trapped in an embedded state on the resinous sliding bearing which is lower in hardness than the bush, precluding a problem of soil accumulation on or between sliding surfaces of the bush and connecting pin. Besides, the hardened surface layer which is higher in hardness than intruding soil can prevent abrasive wear of the bush or connecting pin and enhance durability of these parts even if small fragments of soil get between them.
According to a preferred form of the present invention, the sliding bearing receptacle groove is provided at least in right and left end portions on the inner periphery of the bush, and the resinous sliding bearing is fitted in each one of right and left sliding bearing receptacle grooves. With the arrangements just described, the resinous sliding bearing can be located in right and left end portions of the bush thereby to prevent soil from entering a gap space or clearance between the bush and the connecting pin from outside.
Further, according to another preferred form of the present invention, the resinous sliding bearing is provided with recessed grooves on the inner peripheral side thereof for trapping therein foreign matter coming in from outside. Therefore, soil which has intruded into a gap space between an outer link portion and a bush can be trapped in the recessed grooves on the inner periphery of the sliding bearing to prevent same from getting between the bush and connecting pin.
Further, according to still another preferred form of the present invention, a plural number of the recessed grooves are provided at intervals around the inner periphery of the resinous sliding bearing and extended in an axial direction. With the arrangement just described, the recessed grooves as axial grooves can be provided at uniformly spaced positions around the inner periphery of the resinous sliding bearing to efficiently trap soil or other foreign matter which gets into a gap space between the outer link portion and the bush.
Further, according to the present invention, the recessed grooves on the resinous sliding bearing are filled with a lubricant oil. The lubricant oil in the recessed grooves on the resinous sliding bearing can be supplied, for example, to sliding surfaces between the bush and the connecting pin as well as to sliding surfaces between the resinous sliding bearing and the connecting pin for the purpose of reducing sliding resistance.
Furthermore, according to the present invention, an outer end face of the resinous sliding bearing is held in abutting engagement with the seal member, and the recessed grooves are each opened at one end on the side of the outer end of the resinous sliding bearing and closed at the other end. With the arrangements just described, intruding soil can be trapped into the recessed grooves through the respective open ends, and trapped soil is blocked at the other closed ends of the respective recessed grooves to prevent its intrusion into a gap space between the bush and connecting pin.
Further, according to the present invention, the seal member is composed of an outer lip portion fitted in an outer link portion of a track link, an inner lip portion slidably held in contact with end faces of the bush and the resinous sliding bearing, and a interconnecting bridge portion connected between the outer and inner lip portions substantially in the shape of letter xe2x80x9cMxe2x80x9d.
With the arrangements just described, when the seal member is fitted in position between an outer link portion of a track link and a bush, the outer lip portion can be resiliently abutted against the outer link portion, while the inner lip portion is resiliently abutted against end faces of the bush and resinous sliding bearing. Accordingly, a gap space between the outer link portion and bush can be sealed up by the seal member in good condition.
Furthermore, according to the present invention, the seal member is composed of an annular outer seal member fitted in an outer link portion of a track link and held in abutting engagement with an end face of a bush, and an annular inner seal member accommodated within the outer seal member and held in abutting engagement with the outer seal member and the resinous sliding bearing.
With the arrangements just described, during a vehicular driving operation, the outer seal member of the seal member, which is located on the side of the resinous sliding bearing, is held in abutting engagement with an end face of the bush, while the inner seal member is held in abutting engagement with the sliding bearing. In this state, a gap space between the outer link portion and bush and a gap space between the outer link portion and sliding bearing can be sealed up in a stable state by the inner and outer seal members, respectively.
On the other hand, according to the present invention, the resinous sliding bearing is formed of at least a synthetic resin material selected from an ultra-high molecular weight polyethylene-base resin, a polyether etherketone-base resin, a polyterafluoroethylene-base resin and a polyimide-base resin. With this arrangement, the sliding bearing which is formed of an ultra-high molecular weight polyethylene-base resin, for example, can enjoy higher resistance to abrasive wear and better lubricative characteristics.
Further, according to the present invention, the hardened surface layer is formed of at least a compound selected from borides, nitrides and carbides. In this case, the hardened surface layer can be enhanced in hardness by using a boride compound layer therefor.
Moreover, according to the present invention, the hardened surface layer on the connecting pin is also likely to be formed of a tungsten carbide-base layer by thermal spray coating. In this case, the hardened surface layer can be enhanced in hardness similarly described above.